Continuous wave (CW) Doppler radar motion sensors emit a continuous wave radio frequency (RF) carrier and mix the transmitted RF with the return echoes to produce a difference frequency equal to the Doppler shift produced by a moving target. These sensors do not have a definite range limit (i.e., they can receive signals for both near and far objects, with the received signal being a function of radar cross section). This can lead to false triggers i.e., motion artefact interference. They may also have an undesirably high sensitivity at close range that leads to false triggering.
A pulse Doppler motion sensor is described in U.S. Pat. No. 4,197,537 to Follen et al. A short pulse is transmitted and its echo is self-mixed with the transmitted pulse. The pulse width defines the range-gated region. When the transmit pulse ends, mixing ends and target returns arriving after the end of the transmit pulse are not mixed and are thereby gated out.
A Differential pulse Doppler motion sensor disclosed in U.S. Pat. No. 5,966,090, “Differential Pulse Radar Motion Sensor,” to McEwan, alternately transmits at two different pulse widths. It then subtracts the Doppler responses from each width to produce a range gated “Doppler” sensing region having a fairly constant response versus range.
Impulse radar, such as that described in U.S. Pat. No. 5,361,070, “Ultra-Wideband Radar Motion Sensor,” to McEwan produces a very narrow sensing region that is related to the transmitted pulse width. A two-pulse Doppler radar motion sensor, as described in U.S. Pat. No. 5,682,164, “Pulse Homodyne Field Disturbance Sensor,” to McEwan, transmits a first pulse and after a delay generates a second pulse that mixes with echoes from the first pulse. Thus a range gated sensing band is formed with defined minimum and maximum ranges. UWB radar motion sensors have the disadvantage of not having global RF regulatory acceptance as an intentional radiator. They also have difficulty sensing objects at medium ranges and in some embodiments can be prone to RF interference.
A modulated pulse Doppler sensor is described in U.S. Pat. No. 6,426,716 to McEwan. The range gated microwave motion sensor includes adjustable minimum and maximum detection ranges. The apparatus includes an RF oscillator with associated pulse generating and delay elements to produce the transmit and mixer pulses, a single transmit (TX)/receive (RX) antenna or a pair of separate TX and RX antennas, and an RF receiver, including a detector/mixer with associated filtering, amplifying and demodulating elements to produce a range gated Doppler signal from the mixer and echo pulses.
In U.S. Pat. No. 7,952,515, McEwan discloses a particular holographic radar. It adds a range gate to holographic radar to limit response to a specific downrange region. McEwan states that cleaner, more clutter-free radar holograms of an imaged surface can be obtained, particularly when penetrating materials to image interior image planes, or slices. The range-gating enables stacked hologram technology, where multiple imaged surfaces can be stacked in the downrange direction.
In U.S. Pat. No. 7,994,968, McEwan discloses an RF magnitude sampler for holographic radar. McEwan describes that the RF magnitude sampler can finely resolve interferometric patterns produced by narrowband holographic pulse radar.
In U.S. Patent Application Publication No. 2014/0024917, McMahon et al, describe a sensor for physiology sensing that may be configured to generate oscillation signals for emitting radio frequency pulses for range gated sensing. The sensor may include a radio frequency transmitter configured to emit the pulses and a receiver configured to receive reflected ones of the emitted radio frequency pulses. The received pulses may be processed to detect physiology characteristics such as motion, sleep, respiration and/or heartbeat.
Wearable wristbands such as the Nymi introduce another parameter that can be used in authentication systems—the ECG shape (morphology) that is specific for each user. (https://www.nymi.com/)
US 20100191076 A1 (Aaron Lewicke, Yi Zhang, John D. Hatlestad) describes daytime/nighttime respiration rate monitoring.
U.S. Pat. No. 8,232,866 (William R. McGrath, Ashit Talukder) describes remote long standoff biometric identification using microwave cardiac signals.
U.S. Pat. No. 832,100 (Seth Snyder, Jasper Speicher) describes a Biometric data display system and method.
WO 2003000015 (Mark D Wiederhold, Rodney P Meyer, Steven A Israel, John M Irvine) describes identification by analysis of physiometric variation.
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US 20110040574 (Ho Chung Nicholas Fung, Chu Yong Sang) describes Health Monitoring System with Biometric Identification.
U.S. Pat. No. 6,993,378 (Mark D. Wiederhold, Steven A. Israel, Rodney P. Meyer, John M. Irvine) describes identification by analysis of physiometric variation.
There may be a need to improve sensors and/or their signal processing for sensing such characteristics for identification or authentication.
For authentication and other purposes, it is desirable to be able to identify a person.
The advent of wearable and non-contact physiological and behavioral data capture has led to a need to detect and identify a specific person from their personal biometric “fingerprint”, both to reject data from a another person (impersonation), and to assure compliance or use of those sensors (and potentially attached or associated services or therapies). Such characteristics can be drawn from physiological and behavioral signals.
In addition to detecting that sensor data have been collected from a specific user and their micro and macro environment, it is desirable that a system be able to detect deviations from normal (healthy) signals, and be robust to such changes (e.g., worsening condition or improving condition due to treatment/therapy).